1. Field of the Invention
This invention relates to a sheet conveying device or a sheet discharging device, which is mounted in a recording apparatus, such as a printer mounted, for example, in an information output apparatus, such as a computer, a copier or a facsimile apparatus.
2. Description of the Related Art
In a conventional sheet discharging device mounted in a recording apparatus, such as a printer or the like, a discharging roller, which is rotatably driven by a transmitted driving force, and a spur, which is rotatably driven by the discharging roller in pressure contact therewith, are provided. As shown in FIG. 7, sawtooth tips 51a are formed on the circumference of a spur 51 in order to minimize the spur's contact with a recording surface of a sheet on which an image has been recorded. The tips 51a are formed by pressing a metallic thin plate in a single shot, or by molding.
In the above-described conventional recording apparatus, however, when coated paper, ordinary paper, an OHP (overhead projector) sheet or the like is used as a recording material, ink adhering to the tips 51a of the spur 51 may stain a white region of the sheet, or the surface of the sheet recorded by another color.
The influence of the spur at a sheet discharging portion is greater in the case of a color printer than in the case of a monochromatic (black and white) printer. That is, even a slight amount of ink adhering to the spur becomes in a wet state in contact with unfixed ink having another color after one revolution of the spur to cause color mixture, thereby staining the recorded surface of the sheet.
In a sheet on which it is difficult to fix ink, staining by the ink adhered to the spur is likely to occur because wetting by the ink on the sheet is remarkable. Particularly in an OHP sheet, slip occurs between the spur and the liquid surface of unfixed ink on the sheet, thereby easily producing linear slip traces depending on the relative speed between the spur and the sheet. In an ink-jet-recording color printer, various kinds of recording materials, such as an OHP sheet, ordinary paper and the like, are used in addition to coated paper. Hence, slip traces caused by the spur are remarkably produced on the recorded surface of the sheet, especially when recording is performed on a recording material having low fixability.
FIGS. 8 and 9 schematically illutrate stains produced on the recorded surface of a sheet P by the spur 51. FIG. 8 illustrates stains caused by black ink (Bk) redissolved in wet red ink (R) on the sheet P. FIG. 9 illustrates black points (Bk1), and black lines (Bk2) caused by slip produced on the sheet P having low ink fixability. In FIG. 8, a discharging roller 52 is rotatably driven by a transmitted driving force. The spur 51 is rotatably driven by the discharging roller 52 in pressure contact therewith. FIG. 10 is an enlarged view illustrating the contact portion between the OHP sheet P and the spur 51, and illustrates a state in which black ink (Bk) and green ink (G) adhere to a coated layer C on the OHP sheet P having a thickness of about 80-200 .mu.m, and the tip 51a of the spur 51 slips in the direction of the arrow caused by the green ink.